1. Field of the Invention
The invention relates to an improved expansion screw and particularly an expansion screw for securely anchoring on a solid wall or a hollow wall.
2. Description of the Prior Art
There are a wide variety of expansion screws known in the art. In general, they can be grouped in two types as shown in FIGS. 1 and 2. In FIG. 1, the expansion screw 10 mainly includes a bolt 11 coupling with a washer 12, a nail tube 13 and a compression cone 14. The nail tube 13 has a front section formed an expansion section 131 to couple with the smaller end of the compression cone 14 so that when that expansion screw 10 is inserted into a construction hole 21 of a solid wall 20 (as shown in FIG. 3) the bolt 11 may be turned and tightened to pull the compression cone 14 into the nail tube 13 and force the expansion section 131 to expand outwards to squeeze the inner wall of the construction hole 21 to form anchoring. Then the bolt 11 may be used to hang or support articles. Such type of expansion screw 10 generally is suitable only for solid walls, but is not desirable for brick walls that have cavities inside.
FIG. 2 illustrates another type of conventional expansion screw 10xe2x80x2 which includes a bolt 11xe2x80x2 coupling with a washer 12xe2x80x2 and a nail tube 13xe2x80x2. The nail tube 13xe2x80x2 has a front end fastened to a nut 14xe2x80x2 to engage with the bolt 11xe2x80x2. The front section of the nail tube 13xe2x80x2 forms an expansion section 131xe2x80x2 which has carved slots formed thereon in an annular manner. When the expansion screw 10xe2x80x2 is inserted into a construction hole 21xe2x80x2 of a hollow wall 20xe2x80x2, the expansion section 131xe2x80x2 may be expanded to a greater degree than the expansion screw 10 mentioned above. However, it is still difficult to control the expansion section 131xe2x80x2 to move away from the hollow portion 210xe2x80x2 of the wall 20xe2x80x2. It could happen that the extended expansion section 131xe2x80x2 be located in the hollow portion 210xe2x80x2 as shown in FIG. 4 and result in not secured coupling with the inner wall of the construction hole 21xe2x80x2. In practical constructions, it is often difficult to accurately determine whether the interior of a wall is solid or hollow, hence to nail the expansion screw into a wall often cause construction problems. How to resolve the problems occurred to the conventional expansion screws and to design an improved expansion screw that is suitable for solid walls and hollow walls thereby to effectively overcome the troubles in construction is the goal of the present invention.
The primary object of the invention is to provide an improved expansion screw that is applicable to various types of construction holes formed on a wide variety of solid walls and hollow walls.
Another object of the invention is provide an improved expansion screw that has a plurality of expansion flaps on an expansion section located on the front end of the nail tube to form a double overlap and to generate a double squeeze in the construction hole to achieve a secured fastening.
A further object of the invention is provide an improved expansion screw that has a plurality of expansion sections on the nail tube so that at least one expansion section may be extended to form a tight coupling with the interior structure of the wall to enhance success probability of construction.
In order to achieve the foregoing objects, the invention includes a bolt coupled with a washer and a nail tube which has a front end fastened to a nut. The nail tube has carved slots formed on the middle portion to form at least one expansion section. Between the expansion section and the nut, the nail tube has a plurality of -shaped slots formed thereon. On an inner side of each -shaped slot, there is an expansion flap. Each the -shaped slot borders a longitudinal connection strip to form a bend section. The nail tube beyond the connection strip forms an annular ring with an outer edge formed a plurality of jutting lugs for soldering a nut. The expansion screw thus constructed has at least one expansion section to generate expansion on a plurality of sections.